1. Field of the Invention
This invention relates to a novel synthetic crystalline material MCM-69, comprising a dispersible silica hydrate having acidic surface silanol groups, to its exfoliated products, to a method for their preparation, and to their use in hydrophilic and hydrophobic aggregates and dispersions, such as coatings and catalysts.
2. Description of the Prior Art
In hydrothermal crystallization between about 100 and 180xc2x0 C., piperazine is known to yield a number of siliceous structures, including clathrasils or clathrate group tectosilicates (clathrates), such as ZSM-39, disclosed in U.S. Pat. No. 4,287,166, molecular sieves (e.g., FER-type structures), and layer silicates (e.g., EU-19). Clathrates have been defined as a group of tectosilicates characterized by a structure analogous to gas hydrates (water-clathrates) wherein the oxygens linking non-oxygen framework atoms (T-atoms) in a tectosilicate framework structure are analogized to the hydrogen bonds linking oxygens in the gas hydrates. See, Hydrothermal Chemistry of Zeolites, R. M. Barrer, Academic Press, London (1982). Members of the clathrate group include the mineral melanophlogite as well as dodecasils such as ZSM-39 which typically consist of cages comprising pentagonal rings. Dodecasils, which have a dodecahedral host lattice, are further described in Angew, Chem. Int. Ed. Engl., 21 (1982) No. 3 at pp. 206-207. The clathrates exhibit very limited sorptive and exchange properties, probably owing to their being made up of rings having no more than 6 members. Thus, while certain species may contain relatively large hexakadecahedral or icosahedral cages, sorption of even small molecules is limited because entry into the interior large cages is restricted by the 5-and/or 6-membered rings which make up such cages. Furthermore, the clathrates are characterized by relatively low surface area.
EU-19 was originally synthesized by A. J. Blake, K. R. Franklin, and B. M. Lowe and published in J. Chem Soc., Dalton Trans., 2513 (1988). Designated a crystalline xe2x80x9cpiperazine silicate,xe2x80x9d its structure was determined to contain xe2x80x9csilicate double layers separated by and hydrogen bonded to piperazinium ionsxe2x80x9d [S. J. Andrews, M. Z. Papiz, R. McMeeking, A. J. Blake, B. M. Lowe, K. R. Franklin, J. R. Helliwell, and M. M. Harding, Acta Cryst. B44, 73 (1988)]. Notably, xe2x80x9cEU-19 does not contain any loosely bound or occluded water.xe2x80x9d Moreover, the structure of EU-19 was reported xe2x80x9cto collapse to a product with a few broad peaksxe2x80x9d in its x-ray diffraction (xrd) pattern when the piperazine (pipz) was removed. When heated in air above 300xc2x0 C., EU-19 converted to xe2x80x9ca new silica polymorph EU-20 . . . (which is characterized by) its high thermal stability and its complete lack of sorptive properties.xe2x80x9d
The present invention is directed to a novel crystalline material, named MCM-69, which in its as-synthesized form is characterized by an X-ray diffraction pattern including values substantially as set forth in Table I of the specification and which is believed to have a composition comprising the approximate molar formula: H2O.6SiO2. MCM-69 may also contain small amounts of aluminum, substituting for silicon atoms in the crystalline structure. In general, the atom ratio of Al:Si in MCM-69 will be less than about 0.01, providing an approximate molar formula: H2O.(SiO2)(6xe2x88x92x)(Al2O3)x where x is less than about 0.01. The invention is also directed at the exfoliated products of MCM-69.
It has now been found that piperazine can be substantially removed from a material which appears to have the general topology of EU-19, to obtain a crystalline silica hydrate product, MCM-69, which has a distinctive xrd pattern, which does not convert to EU-20 on heating above 300xc2x0 C., and which appears to be comprised of single, crystalline layers of silica having a high surface concentration of reactive silanols. Specifically, in the ideal MCM-69 structure, one out of every three Si atoms in MCM-69 appears to contain a silanol group. The silanols can be reacted with a variety of organic and inorganic chemicals to generate a substantial and diverse series of useful products.
The invention further resides in a method for the preparation of MCM-69, in the characteristic exfoliation of MCM-69, and in its use and that of its exfoliated products in the preparation of hydrophilic and hydrophobic aggregates and dispersions.